Can large dermoid ovarian cyst cause mood issues? hostility, sadness, mood swings. i'm otherwise well-medicated and seen by a psychiatrist.

No: How large is it? See your gynecologist for further evaluation and treatment, but does not cause mood issues.

Highly unlikely: If you are experiencing mood swings, hostility, and sadness, you should see your psychiatrist as soon as possible. It is more likely that you need an adjustment in your psychiatric medications and/or more intensive counseling and/or close monitoring by your psychiatrist. It is possible that the knowledge of having large dermoid cyst could affect your mood.

Poss but unlikely: Dermoids are interesting ovarian tumors, and can have just about any kind of tissue in them, including functioning thyroid and nervous tissue, although it's rare. Dermoids will not go away on their own, and if it is large, it should be removed.